In general, this invention relates to a method for applying a tail wrap to a wound electrochemical cell, in particular, to an electrochemical cell for a lead acid battery. Such an electrochemical cell will have flexible strip members wound into a generally cylindrical or jelly roll configuration to form a wound cell pack. The flexible strip members will include a positive electrode, a negative electrode, and one or more separators. The flexible strip members are typically wound about a mandrel and secured in their wound configuration so that they may be inserted into a cell casing with ease.
Various techniques and apparatus for securing the wound configuration of the flexible strip members into a wound cell pack are known. In U.S. Pat. No. 4,802,275 hot melt glue is used to secure one of the separators or the negative electrode to itself during the end of the winding operation. However, this securing technique is difficult to achieve when using a separator which will not bond readily to the hot melted glue. Also, when hot melt glue is applied to one of the electrodes to secure the cell pack, the danger arises that the glue on the electrode could adhere or stick to various other elements. As it is necessary to deposit the hot melted glue outside of the winding operation, the time required before attachment to the electrode can affect the reliability of the glue bond. Thus, the glue can dry quickly and prevent a secure attachment. Using an electrode for the final wrap of the wound cell pack can leave the electrode exposed for damage upon insertion into the cell casing. Also, the final capacity of the cell can be adversely affected by using the melt glue.
Another method for securing a wound cell pack is shown in U.S. Pat. No. 4,402,784. In this patent, an end of one of the separators of the wound cell pack is heat sealed to itself during the last part of the wind by means of flexible heat sealing fingers. This method of securing a wound cell pack cannot be used with all separators. Certain separators are not easily bondable to themselves or to organic materials. In particular, separators which are formed of fiber glass or a glass mat reject heat sealing back onto themselves.
In the past, other securing techniques for cell packs have been used which require the attachment of additional items to the wound cell pack to maintain its configuration. For example, an operator can manually apply a securing strip of suitable plastic tape to the outside diameter of the wound cell pack prior to ejection of the wound roll from the winding mandrel. This method of securement results in a relatively slow rate of production and a high cost of operation due to the manual operation. This method slows down the rate at which the wound cell packs are produced. Factors such as operator error and variations in operator technique can also influence the end product.
U.S. Pat. No. 4,064,725 discloses a further prior art approach to securing the wound cell pack. In this patent, one end of a piece of tail wrap material is attached to one of the separators by tape. The other end of the piece of tail wrap material has a binder comprising double-sided tape attached to it. As the tail wrap material is wrapped around the cell pack, it adheres onto itself with the aid of the binder to constrict the wound cell pack to its generally cylindrical configuration. This patent, however, also requires manual operation to secure the wound cell pack. It is necessary for the tail wrap to be taped initially to the separator and then it is necessary to apply the binder or double-sided tape to the tail wrap before it can be wrapped around the wound cell pack. This method of securing the wound cell pack is also difficult to achieve in cell packs where the separator resists the tape attachment. If the tape adhesive does not adhere properly to the separator, failure in securing the wound cell pack would result.